Peripheral nerve injury may result in the development of chronic intractable pain. Some patients prove unresponsive to conservative pain management techniques. Peripheral Nerve Stimulation (PNS) has developed as a successful therapy for pain management when the pain is known to result from a specific nerve. PNS is based in part on the Melzack-Wall gate control theory of pain. Sweet and Wespic first used electrical stimulation of peripheral nerves in the 1960s to mask the sensation of pain with a tingling sensation (paresthesia) caused by the electrical stimulation. Subsequent refinements in the technology, surgical technique and patient selection have led to improved long term results.
Efforts have been made to treat psychiatric disorders with peripheral/cranial nerve stimulation. Recently, partial benefits with vagus nerve stimulation in patients with depression have been described in U.S. Pat. No. 5,299,569. Another example of electrical stimulation to treat depression is described in U.S. Pat. No. 5,470,846, which discloses the use of transcranial pulsed magnetic fields to treat depression. Yet further, U.S. Pat. No. 5,263,480 describes that stimulation of the vagus nerve may control depression and compulsive eating disorders and U.S. Pat. No. 5,540,734 teaches stimulation of the trigeminal or glossopharyngeal nerves for psychiatric illness, such as depression.
Another example of peripheral nerve stimulations include, for example, stimulating the C2 dermatome area to treat occipital neuralgia, which may be defined generally as an intractable headache originating in the back of the head in the vicinity of the C2 dermatome area (U.S. Pat. No. 6,505,075). This method of delivering electrical stimulation energy to the C2 dermatome area to treat occipital neuralgia involves positioning stimulation electrodes of an implantable electrical stimulation lead with at least one electrode in the fascia superior to in a subcutaneous region proximate the C2 dermatome area.
Yet further, the use of electrical stimulation for treating neurological diseases, including such disorders as movement disorders including Parkinson's disease, essential tremor, dystonia, and chronic pain, have also been widely discussed in the literature. It has been recognized that electrical stimulation holds significant advantages over lesioning since lesioning destroys the nervous system tissue. In many instances, the preferred effect is to modulate neuronal activity. Electrical stimulation permits such modulation of the target neural structures and, equally importantly, does not require the destruction of nervous tissue. Such direct electrical stimulation procedures include electroconvulsive therapy (ECT), transcranial direct current stimulation (tDCS) and vagal nerve stimulation (VNS). In addition, indirect cortical (brain) electrical stimulation can be achieved via transcranial magnetic stimulation (TMS).
Traditional treatment options, for some forms of intractable pain (occipital pain, traumatic brain injury) that have proven to be resistant to medications, usually involve chemical, thermal or surgical ablation procedures following diagnostic local anesthetic blockade. Surgical approaches include neurolysis or nerve sectioning of either the C2 dermatome area in the occipital scalp or at the upper cervical dorsal root exit zone (extradural). Foraminal decompressions of C2 roots as well as C2 ganglionectomy have also been effective in reported cases.
Transcranial magnetic stimulation (TMS) was first introduced in 1985. TMS provided a non-invasive, safe and painless method of activating the human motor cortex and assessing the integrity of the central motor pathways. Since its introduction, the use of TMS in clinical neurophysiology, neurology, neuroscience, and psychiatry has spread widely.
TMS is based on the principle of electromagnetic inductions. If a pulse of current passing through a coil placed over a person's head has sufficient strength and short enough duration, rapidly changing magnetic pulses are generated that penetrate scalp and skull to reach the brain with negligible attenuation. These pulses induce a secondary ionic current in the brain. The site of stimulation of a nerve fiber is the point along its length at which sufficient current to cause depolarization passes through its membrane. Depending on the stimulation setting, single stimuli can either excite or inhibit neuronal functions.
Magnetic stimulation provides a non-invasive method for modulating nerve function and chronic pain management. Current methods of magnetic treatment for pain can be delivered via either static or dynamic magnetic field. While the efficacy of static magnetic field treatment such as magnetic bracelets has yet to be substantiated, studies involving the use of repetitive transcranial magnetic stimulation (dynamic magnetic flux) have yielded appreciable evidence support the merits of the device in relieving pain. Aside from stimulating the brain, the utilization of dynamic magnetic flux in transcutaneous stimulation for pain relief has not been fully explored. This under-utilization is the result of a number of issues: 1) the current commercially-available magnetic stimulators are physically very bulky; 2) the coils usually require additional cooling units to prevent overheating; 3) the devices are too expensive to be accessible to the general public; and 4) operating the device requires special training and clinical privilege. These physical limitations, cost and the requirement of special training restrict the current scope of use of this non-invasive means of pain management outside of healthcare facilities.
Accordingly, the need remains for a device that is affordable and easy to use that makes tMS, an effective tool for management of chronic pain, readily available.